1. Field of the Invention
The present invention relates to a product ejecting apparatus and method for an injection molding machine.
2. Description of the Related Art
Conventionally, for example, a disc-molding machine is adapted to mold a disc by the steps of heating and melting within a heating cylinder a resin serving as a molding material; charging the molten resin into a cavity of a disc-making mold assembly serving as a mold apparatus; and allowing to set through cooling.
FIG. 1 is a sectional view showing a main portion of a conventional injection molding machine. FIG. 2 is a diagram showing operation of a conventional cut punch/ejector unit. In FIG. 2, the x-axis represents time, and the y-axis represents projection amount.
In FIG. 1, reference numeral 11 denotes a movable platen. An unillustrated movable mold unit is attached to a front end face (right-hand end face in FIG. 1) S1 of the movable platen 11. A cut punch/ejector unit 12 is attached to a rear end face (left-hand end face in FIG. 1) S2 of the movable platen 11. The movable mold unit includes a base plate and a mirror-finished block attached to the base plate.
An unillustrated stationary platen is disposed in front (right-hand side in FIG. 1) of the movable platen 11. An unillustrated stationary mold unit is attached to the stationary platen in such a manner as to face the movable mold unit. The stationary mold unit includes a base plate, a mirror-finished block attached to the base plate, and a stamper attached to the mirror-finished block.
An unillustrated mold-clamping unit is disposed in the rear (left-hand side in FIG. 1) of the movable platen 11. The mold-clamping unit is adapted to advance/retreat (move rightward/leftward in FIG. 1) the movable platen 11, thereby closing, clamping, or opening the disc-making mold assembly.
A disc is formed in the following manner. First, the mold-clamping unit is operated so as to advance (move rightward in FIG. 1) the movable platen 11, thereby closing the mold. Subsequently, the mold-clamping unit is operated further to generate a mold-clamping force for clamping the mold. At this time, the mirror-finished block of the movable mold unit and that of the stationary mold unit define a cavity therebetween. Then, molten resin is injected through the injection nozzle of an unillustrated injection unit so as to fill the cavity, followed by cooling to form a disc blank. After the resin is completely cooled and before the resin sets, the cut punch/ejector unit 12 is operated so as to punch a hole in the disc blank, thereby forming a disc. Subsequently, the mold-clamping unit is operated so as to retreat (move leftward in FIG. 1) the movable platen 11, thereby opening the mold. Also, the cut punch/ejector unit 12 is operated so as to advance an unillustrated ejector pin, thereby knocking out the disc from the mirror-finished block of the movable mold unit; i.e., releasing the disc from the mold.
Next, the cut punch/ejector unit 12 will be described.
A housing accommodation hole 14 is formed in the movable platen 11 in such a manner as to open at the rear end face S2. An annular bearing housing 15 is attached to the rear end face S2 so as to cover the housing accommodation hole 14. A closed-bottomed cylindrical housing 16 is attached to the front end (right-hand end in FIG. 1) of the bearing housing 15 while being accommodated within the housing accommodation hole 14. Two bearings 17 and 18 are disposed within the bearing housing 15. A first ball nut 19 is rotatably supported by the bearings 17 and 18. The first ball nut 19 has a flange portion 21 at the rear end (left-hand end in FIG. 1) thereof. An annular driven pulley 22 is fixedly attached to the flange portion 21. A second ball nut 23 is attached to the pulley 22. The second ball nut 23 has a flange portion 24 at the front end thereof. The flange portion 24 is fixedly fitted into the pulley 22.
A servomotor 26 serving as drive means is disposed. A timing belt 29 is looped around and extends between the driven pulley 22 and a drive pulley 28 attached to an output shaft 27 of the servomotor 26. The pulleys 22 and 28 and the timing belt 29 constitute rotation transmission means. Reference numeral 31 denotes an encoder serving as a rotational-speed detector for detecting the rotational speed of the servomotor 26.
The first ball nut 19 has a stepped portion 33 adjacent to the rear end of the bearing 17, while a cylindrical positioning ring 34 is disposed on the outer circumferential surface of the first ball nut 19 adjacent to the front end of the bearing 18. The front end of the first ball nut 19 and a positioning nut 35 are screw-engaged. The positioning nut 35 is tightened so as to hold the bearings 17 and 18 by means of the stepped portion 33 and the positioning ring 34, thereby positioning the first ball nut 19 with respect to the bearing housing 15.
A hole 43 is formed in the movable platen 11 in such a manner as to extend therethrough. A cylindrical cut punch unit 37 is disposed within the hole 43, the first ball nut 19, and the bearing housing 15 such that it can reciprocate. The cut punch unit 37 includes, from the rear end to the front end, a ball screw portion 38 having, for example, right-hand threads formed on the outer circumferential surface thereof, a spline portion 39 having a spline formed on the outer circumferential surface thereof, and a cut punch rod 44. Right-hand threads are formed on the inner wall surface of the first ball nut 19 so as to establish screw engagement between the first ball nut 19 and the ball screw portion 38. A spline is formed on the housing 16 so as to establish spline engagement between the housing 16 and the spline portion 39. A cylindrical cut punch serving as a working member is disposed within the movable mold unit. The rear end of the cut punch is connected to the front end of the cut punch rod 44. The first ball nut 19 and the ball screw portion 38 constitute motion conversion means for converting rotary motion of the first ball nut 19 to linear motion of the ball screw portion 38. The spline portion 39 constitutes rotation restriction means for restricting rotation of the cut punch unit 37.
Two guide bars 45 and 46 are attached to the rear end face of the bearing housing 15 in such a manner as to extend rearward. A plate 47 is disposed on the guide bars 45 and 46 such that it can reciprocate along the same. A ball screw 48 is attached to the plate 47 in such a manner as to extend forward. Inverse threads with respect to the threads formed on the outer circumferential surface of the ball screw portion 38; for example, left-hand threads, are formed on the outer circumferential surface of the ball screw 48. For example, left-hand threads are formed on the inner wall surface of the second ball nut 23 so as to establish screw engagement between the second ball nut 23 and the ball screw 48. An ejector rod 51 is formed at the front end of the ball screw 48 in such a manner as to extend forward through the cut punch unit 37. An ejector pin is disposed within the cut punch. The rear end of the ejector pin is connected to the front end of the ejector rod 51. The second ball nut 23 and the ball screw 48 constitute motion conversion means for converting rotary motion of the second ball nut 23 to linear motion of the ball screw 48. The plate 47 constitutes rotation restriction means for restricting rotation of the ball screw 48.
Next, operation of the thus-configured cut punch/ejector unit 12 will be described.
First, drive control means of an unillustrated controller causes the servomotor 26 to rotate in the regular direction. Rotation in the regular direction is transmitted to the first and second ball nuts 19 and 23 via the output shaft 27, the pulley 28, the timing belt 29, and the pulley 22. Accordingly, the cut punch unit 37 is caused to advance, thereby causing the cut punch to advance, as represented by line L2 in FIG. 2. Thus, the cut punch punches a hole in the disc blank. At this time, the ball screw 48 is caused to retreat, thereby causing the ejector pin to retreat, as represented by line L1 in FIG. 2.
At timing t1, the drive control means causes the servomotor 26 to stop rotating and resume rotation in the reverse direction. Rotation in the reverse direction is transmitted to the first and second ball nuts 19 and 23 via the pulley 28, the timing belt 29, and the pulley 22. Accordingly, the cut punch unit 37 is caused to retreat, thereby causing the cut punch to retreat, as represented by line L2. Thus, the cut punch comes off the punched hole. At this time, the ball screw 48 is caused to advance, thereby causing the ejector pin to advance, as represented by line L1. Thus, the ejector pin knocks out the disc from the mold. Subsequently, when timing t2 is reached, the drive control means causes the servo motor 26 to stop rotating.
Through use of the servomotor 26 for punching a hole in the disc blank, positional accuracy of the cut punch can be improved.
However, according to this conventional disc-making mold assembly, when the ejector pin projects so as to knock out the disc from the mold, the cut punch is caused to retreat. Thus, the cut punch fails to hold the disc. In other words, the cut punch and the ejector pin cannot be operated concurrently.
Therefore, in order to hold the disc for a predetermined period of time by means of the cut punch, knock-out operation of the ejector pin must be delayed accordingly, causing an increase in molding cycle time.
An object of the present invention is to solve the above-mentioned problems in the conventional disc-making mold assembly and to provide a product ejecting apparatus and method for an injection molding machine which apparatus and method allow a working member and an ejector pin to operate concurrently to thereby shorten molding cycle time.
To achieve the above object, the present invention provides a product ejecting apparatus for an injection molding machine, comprising: a first drive unit; a first transmission unit connected to the first drive unit, wherein a rotation of the first drive unit results in a rotation of the first transmission unit; a second drive unit; a second transmission unit connected to the second drive unit, wherein a rotation of the second drive unit causes a rotation of the second transmission unit; an ejector pin configured to reciprocate based upon a motion of the first transmission unit; and a working member connected to the second transmission unit, wherein a movement of the second transmission unit results in reciprocating movement of the working member.
Through operation of the first drive means, the first transmission member is caused to reciprocate, thereby causing the ejector pin to reciprocate. Through operation of the second drive means, the second transmission member is caused to reciprocate, thereby causing the working member to reciprocate.
Accordingly, when the ejector pin is caused to project in order to knock out a molded product from the mold, the working member can remain at the advance position of its stroke to thereby hold the molded product. In other words, the working member and the ejector pin can be operated concurrently.
Thus, there is no need for delaying knock-out operation of the ejector pin in order to hold a molded product by means of the working member, thereby shortening molding cycle time.